The present invention relates generally to the replacement of underground pipes, and more particularly, to methods and apparatus for replacing fracturable pipes with new pipes which may be of the same size as, or larger than, the old pipes. Still more particularly, the present invention relates to methods and apparatus for replacing existing sewer pipes, water pipes, gas mains, or the like by first ripping the existing pipes to allow the passage of moisture therethrough, then allowing existing sewage and water to fill the ripped pipe and then to flow into the earth formation surrounding the pipe to soften the surrounding earth formation. Upon softening the earth formation surrounding the ripped existing pipe, the existing pipe is then crushed and the debris or shards forced outwardly into the surrounding softened earth formation thereby forming a bore of an appropriate size to pull the replacement pipe into the bore.
It is often necessary repair or replace underground pipes which have lost their fluid-carrying capacity or integrity due to age, the action of corrosive substances, or the effects of other deleterious conditions or hazards. Often repair or replacement is necessary to prevent the fluid which is passing through the pipe to leak into the surrounding earth or other environment. Such leakage could lead to contamination of the surrounding soil or subterranean potable water sources or supplies, for example in the case of underground sewer lines, or to contamination of the fluids carded within the underground pipes, for example in the case of underground water lines. Such leakage could also lead to potentially destructive conditions, placing property and health at risk, for example in the case of underground gas mains. If an underground natural gas main were to leak and allow gas to escape, such leakage could lead to an explosive accumulation of gases in a subterranean reservoir or other formation.
Repair or replacement also sometimes becomes necessary to restore the fluid-carrying capacity of the underground pipes. A sewer line which has become decomposed or broken, often cannot carry the volume of material for which it was designed. This can lead to temporary backups in the event the sewer system becomes deluged by an unusual event, such as a storm, or eventually to complete blockages.
One technique used for replacing underground pipes has been to cut or slit them longitudinally by pulling a cutting tool through the pipes; expanding the resulting segments outwardly with an expanding tool, which may also comprise the cutting tool, to make room for the new pipes; and pulling the new pipe into the space thus created, typically behind and along with the expanding or expanding/cutting tool. Such a technique is useful particularly for pipes made of materials such as steel which do not normally fracture into irregularly-shaped pieces or shards when engaged by a blow or like impact. These techniques may be used to replace an old pipe with one of an equal or larger diameter, if desired. An example of this type of technique is disclosed in U.S. Pat. No. 4,903,406 to Schosek et al. That patent disclose a pipe splitter having a cutting wheel adapted for cutting a pipe, such as a black iron pipe, along a single longitudinal path when pulled through the pipe. An expander may be pulled through the split pipe for spreading the pipe apart, and a new pipe pulled into place trailing the expander. Another example of this type of technique is disclosed in U.S. Pat. No. 3,181,302 to Lindsay. The Lindsay apparatus is adapted to split or cut the existing pipe longitudinally at two locations, for example into two halves, rather than at one location as in the Schosek patent. Examples of other devices used in the past for cutting, ripping, or splitting pipes, casing, tubing, or the like are found in U.S. Pat. Nos. 642,367; 1,001,205; 1,519,882; 1,618,368; 2,502,711; 2,638,165; 2,834,106; 2,947,253; 2,983,042; and 3,023,040.
Another technique used in the past for replacing underground pipes with the same or larger diameter pipes, if desired, has been to burst them from the inside by pulling or pushing a bursting tool through the pipes; expanding the resulting pipe fragments outwardly with an expanding tool, which may also comprise the bursting tool, to make room for the new pipe; and pulling the new pipe into the space thus created, typically behind and along with the expanding or expanding/bursting tool. Such a technique is useful particularly for pipes made of materials such as concrete, tile, or cast iron, which normally fracture into irregularly-shaped pieces or shards when engaged by a blow or like impact. An example of a system utilizing this type of technique is disclosed in U.S. Pat. Nos. 4,505,302; 4,720,211; and 4,738,565 to Streatfield et al. The pipe bursting tool of the Streatfield patents is adapted to engage the interior of the pipe to burst it, and to force the pipe fragments outwardly around the circumference of the tool to create a space for the new pipe, at least a portion of the outward forcing of the pipe fragments occurring at the same time the pipe is destroyed by the outwardly directed fracturing or bursting action.
U.S. Pat. No. 4,507,019 to Thompson discloses another pipe replacement system of the latter type, including a power system for imparting rotation as well as linear movement to an expansion and replacement mandrel as it is moved through the old pipe. The expansion replacement mandrel of the Thompson system includes a plurality of hard metal boring buttons of a material such as tungsten carbide to score the internal surface of the existing pipe as the mandrel is rotated and forced through the pipe. The Thompson system, like the Streatfield system, engages the inside diameter of the existing pipe to destroy it before initially fracturing it outwardly, i.e., by bursting it. The Streatfield and Thompson patents all disclose expanding the pipe fragments radially outwardly to cream a large enough space for pulling in a replacement pipe for the same or larger diameter behind, and along with, the respective bursting tools.
Other systems of this type for replacing an existing pipe, that is, systems relying on bursting the existing pipe from the inside, are disclosed in U.S. Pat. Nos. 4,634,313; 4,648,746; 4,674,914; 4,693,404; 4,732,222; and 4,767,236.
Another technique for replacing an existing pipeline is disclosed in U.S. Pat. No. 4,886,396 to Akesaka. Akesaka discloses apparatus and methods for advancing a shield tunneling machine from one end of the existing pipeline to the other, thereby excavating the existing pipeline with rotating cutters, and placing a new pipeline in the excavated spot while the machine is advanced. The shield tunneling machine of Akesaka may have a diameter larger than the diameter of the existing pipe, so it may excavate not only the existing pipe but also some of the surrounding ground.
A self-propelled pneumatic burrowing device is disclosed in U.S. Pat. No. 4,100,980 to Jenne. The Jenne device includes an axially reciprocating percussion plunger disposed inside a tubular casing so as to strike a percussion head at the forward end of the casing, thereby advancing the device through the ground by crushing and/or displacing the material in the path of the device.
U.S. Pat. No. 5,112,158 by McConnell, the inventor of the present invention, discloses an underground pipe replacement method and apparatus which first crushes the existing pipe entirely inwardly, or imploding it, to destroy it. The surrounding shards are then forced outwardly into the surrounding soil, creating a bore large enough to accommodate a replacement pipe at least as large as, or larger than, the old pipe. The new pipe is pulled into place substantially simultaneously with the expansion of the bore. The crushing tool includes a plurality of blades tapered outwardly and forwardly with a connecting rod connecting the crushing tool to an expanding plug. The expanding plug includes a conical nose for expanding the crushed pipe fragments into the surrounding soil and is pulled through the ground behind and along with the crushing tool, pulling with it the new pipe.
The prior art techniques which utilize apparatus that must be passed through the earth surrounding the old pipe or which require that the shards of the pipe be pressed into the surrounding earth have the common difficulty of passing through the surrounding earth formation where the earth formation surrounding the old pipe is extremely hard and imposes substantial resistance to the passage of the replacement apparatus through the earth or the expansion of the fragments or shards into the surrounding earth formation. Earth formations made of caliche, sandy clay with rock, extremely dry soil, or hard clay often are like concrete substantially increasing the amount of force required to pull tools through the old pipe.
The present invention overcomes the deficiencies of these prior art methods and apparatus.